KR20120047774A - Method and apparatus of transmitting control information for inter-cell interference in wireless communication system - Google Patents

Abstract

PURPOSE: A method and an apparatus for transmitting control information for inter-cell interference in a wireless communication system are provided to efficiently reduce intercell interference in the communication environment of a heterogeneous network. CONSTITUTION: A method for reducing intercell interference is determined. One of precoding information or antenna information according to time frequency resource is transmitted based on the method for reducing intercell interference to a second base station. The precoding information directs a PMI(Precoding Matrix Indicator) which is used through a first base station according to a subframe or a PMI which is used according to the subframe through a second base station. The precoding information is composed of a bit-map based on the total number of PMI.

Description

Method and apparatus for transmitting control information for reducing inter-cell interference in wireless communication system {METHOD AND APPARATUS OF TRANSMITTING CONTROL INFORMATION FOR INTER-CELL INTERFERENCE IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting control information for reducing inter-cell interference in a wireless communication system.

The next generation multimedia wireless communication system, which is being actively researched recently, requires a system capable of processing and transmitting various information such as video, wireless data, etc., out of an initial voice-oriented service. The fourth generation of wireless communication, which is currently being developed after the third generation of wireless communication systems, aims to support high-speed data services of downlink 1 Gbps (Gigabits per second) and uplink 500 Mbps (Megabits per second). The purpose of a wireless communication system is to enable a large number of users to communicate reliably regardless of location and mobility. However, a wireless channel is a path loss, noise, fading due to multipath, inter-symbol interference (ISI) or mobility of UE. There are non-ideal characteristics such as the Doppler effect. Various techniques have been developed to overcome the non-ideal characteristics of the wireless channel and to improve the reliability of the wireless communication.

The current wireless communication environment seeks to diversify communication methods and devices in order to satisfy differentiated service requirements. In the next generation mobile communication system, the demand for data traffic is expected to increase rapidly. Accordingly, a communication method for preventing a large amount of data traffic from being concentrated on one node is under development. For example, a communication method for distributing traffic to a plurality of base stations or a plurality of nodes has been studied, and a communication method using a heterogeneous network is one of the main research objects. Basically, heterogeneous network refers to a communication environment in which a base station having a relatively small service coverage coexists in a service coverage of an existing base station.

In a heterogeneous communication environment, inter-cell interference (ICI) may occur between base stations. Inter-cell interference may operate on femto user equipment or pico user equipment, which are generally serviced by a femto cell or pico cell having a small service coverage from a macro cell. . In order to solve such intercell interference problem, a time domain based solution and a frequency domain based solution have been proposed. For time domain based solution, refer to 3GPP-RAN WG1 # 62bis R1-105750. However, only the time domain based solution or the frequency domain based solution cannot effectively remove the inter-cell interference.

There is a need for a method for efficiently solving the intercell interference problem between base stations in a heterogeneous network communication environment.

An object of the present invention is to provide a method and apparatus for transmitting control information for reducing inter-cell intereference (ICI) in a wireless communication system.

In one aspect, a method of transmitting control information by a first base station in a wireless communication system is provided. The control information transmission method includes determining a method for reducing inter-cell interference and transmitting any one of precoding information or antenna information for each time frequency resource to a second base station based on the determined inter-cell interference reduction method.

The precoding information may indicate a precoding matrix indicator (PMI) that the first base station uses for each subframe or a PMI that the second base station can use for each subframe.

The precoding information may be configured as a bitmap based on the total number of PMIs.

The precoding information may include an index of at least one PMI and the number of PMIs based on the at least one PMI.

The precoding information may include an index of at least one PMI and a threshold based on the at least one PMI.

The antenna information may indicate an antenna that the first base station uses for each subframe or an antenna that the second base station can use for each subframe.

The method for transmitting control information may include receiving antenna interference information measured by terminals serviced by the second base station from the second base station when the antenna information indicates an antenna used by the first base station for each subframe. In addition, the antenna information may be based on the received antenna interference information.

In the control information transmission method, when the antenna information indicates an antenna that can be used by the second base station for each subframe, the antenna information received by the terminals serviced by the first base station or directly received antenna interference information The method may further include acquiring, wherein the antenna information may be based on the received or acquired antenna interference information.

The antenna information may be configured as a bitmap based on the total number of antennas.

The second base station may allocate a downlink resource to the terminal based on the received precoding information or antenna information.

The second base station may communicate with the terminal through a downlink resource allocated to the terminal.

The first base station is a base station for providing a service to a macro cell (macro cell), the second base station is a femto cell (femto cell) or pico cell (service coverage) is included in the service coverage of the macro cell ( It may be a base station providing a service to a pico cell).

In another aspect, a first base station is provided in a wireless communication system. The first base station includes a radio frequency (RF) unit for transmitting or receiving a radio signal, and a processor connected to the RF unit, wherein the processor determines a method for reducing inter-cell interference and based on the determined inter-cell interference reduction method. In this case, any one of precoding information or antenna information for each time frequency resource is configured to be transmitted to the second base station.

Inter-cell interference can be efficiently reduced in heterogeneous network communication environments.

1 is a wireless communication system.
2 shows a structure of a radio frame in 3GPP LTE.
3 shows an example of a resource grid for one downlink slot.
4 shows a structure of a downlink subframe.
5 shows a structure of an uplink subframe.
6 shows an example of a heterogeneous network communication environment.
7 illustrates an embodiment of a time domain based solution for reducing intercell interference in a heterogeneous network communication environment.
8 shows an air interface structure of layer 2 or more in 3GPP LTE.
9 illustrates an embodiment of a frequency domain based solution for reducing intercell interference in a heterogeneous network communication environment.
10 shows an example of a PMI index for each subband of a macro cell forming a beam in a pico cell direction.
11 shows an embodiment of PMI usage information according to the proposed method for transmitting control information for reducing inter-cell interference.
12 shows an embodiment of antenna usage information according to a method for transmitting control information for reducing inter-cell interference.
13 shows an embodiment of a method for transmitting control information for reducing inter-cell interference.
14 is a block diagram of a wireless communication system in which an embodiment of the present invention is implemented.

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various wireless communication systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA), or the like. IEEE 802.16m is an evolution of IEEE 802.16e and provides backward compatibility with systems based on IEEE 802.16e. UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is part of Evolved UMTS (E-UMTS) using Evolved-UMTS Terrestrial Radio Access (E-UTRA), which employs OFDMA in downlink and SC in uplink -FDMA is adopted. LTE-A (Advanced) is the evolution of 3GPP LTE.

For clarity, the following description focuses on LTE-A or IEEE 802.16, but the technical spirit of the present invention is not limited thereto.

1 is a wireless communication system.

The wireless communication system 10 includes at least one base station (BS) 11. Each base station 11 provides a communication service for a particular geographic area (generally called a cell) 15a, 15b, 15c. The cell may again be divided into multiple regions (referred to as sectors). The UE 12 may be fixed or mobile, and may include a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, and a PDA. (Personal Digital Assistant), a wireless modem (wireless modem), a handheld device (handheld device) may be called other terms. The base station 11 generally refers to a fixed station communicating with the terminal 12, and may be referred to as other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like. have.

A terminal typically belongs to one cell, and a cell to which the terminal belongs is called a serving cell. A base station that provides a communication service for a serving cell is called a serving BS. Since the wireless communication system is a cellular system, there are other cells adjacent to the serving cell. Another cell adjacent to the serving cell is called a neighbor cell. A base station that provides communication service for a neighbor cell is called a neighbor BS. The serving cell and the neighbor cell are relatively determined based on the terminal.

This technique can be used for downlink or uplink. In general, downlink means communication from the base station 11 to the terminal 12, and uplink means communication from the terminal 12 to the base station 11. In downlink, the transmitter may be part of the base station 11 and the receiver may be part of the terminal 12. In uplink, the transmitter may be part of the terminal 12 and the receiver may be part of the base station 11.

The wireless communication system is any one of a multiple-input multiple-output (MIMO) system, a multiple-input single-output (MIS) system, a single-input single-output (SISO) system, and a single-input multiple-output (SIMO) system. Can be. The MIMO system uses a plurality of transmit antennas and a plurality of receive antennas. The MISO system uses multiple transmit antennas and one receive antenna. The SISO system uses one transmit antenna and one receive antenna. The SIMO system uses one transmit antenna and multiple receive antennas. Hereinafter, the transmit antenna means a physical or logical antenna used to transmit one signal or stream, and the receive antenna means a physical or logical antenna used to receive one signal or stream.

2 shows a structure of a radio frame in 3GPP LTE.

This is described in Section 5 of 3rd Generation Partnership Project (3GPP) TS 36.211 V8.2.0 (2008-03) "Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)". Reference may be made. Referring to FIG. 2, a radio frame consists of 10 subframes, and one subframe consists of two slots. Slots in a radio frame are numbered with slots # 0 through # 19. The time taken for one subframe to be transmitted is called a Transmission Time Interval (TTI). TTI may be referred to as a scheduling unit for data transmission. For example, one radio frame may have a length of 10 ms, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

One slot includes a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols in the time domain and a plurality of subcarriers in the frequency domain. The OFDM symbol is used to represent one symbol period since 3GPP LTE uses OFDMA in downlink, and may be called a different name according to a multiple access scheme. For example, when SC-FDMA is used as an uplink multiple access scheme, it may be referred to as an SC-FDMA symbol. A resource block (RB) includes a plurality of consecutive subcarriers in one slot in resource allocation units. The structure of the radio frame is merely an example. Accordingly, the number of subframes included in the radio frame, the number of slots included in the subframe, or the number of OFDM symbols included in the slot may be variously changed.

3GPP LTE defines that one slot includes 7 OFDM symbols in a normal cyclic prefix (CP), and one slot includes 6 OFDM symbols in an extended CP. .

A wireless communication system can be largely divided into a frequency division duplex (FDD) system and a time division duplex (TDD) system. According to the FDD scheme, uplink transmission and downlink transmission are performed while occupying different frequency bands. According to the TDD scheme, uplink transmission and downlink transmission are performed at different times while occupying the same frequency band. The channel response of the TDD scheme is substantially reciprocal. This means that the downlink channel response and the uplink channel response are almost the same in a given frequency domain. Therefore, in a TDD based wireless communication system, the downlink channel response can be obtained from the uplink channel response. In the TDD scheme, the uplink transmission and the downlink transmission are time-divided in the entire frequency band, and thus the downlink transmission by the base station and the uplink transmission by the terminal cannot be simultaneously performed. In a TDD system in which uplink transmission and downlink transmission are divided into subframe units, uplink transmission and downlink transmission are performed in different subframes.

3 shows an example of a resource grid for one downlink slot.

The downlink slot includes a plurality of OFDM symbols in the time domain and N _RB resource blocks in the frequency domain. The number N _RB of resource blocks included in the downlink slot depends on the downlink transmission bandwidth set in the cell. For example, in the LTE system, N _RB may be any one of 60 to 110. One resource block includes a plurality of subcarriers in the frequency domain. The structure of the uplink slot may also be the same as that of the downlink slot.

Each element on the resource grid is called a resource element. Resource elements on the resource grid may be identified by an index pair (k, l) in the slot. Where k (k = 0, ..., N _RB × 12-1) is the subcarrier index in the frequency domain, and l (l = 0, ..., 6) is the OFDM symbol index in the time domain.

Here, an exemplary resource block includes 7 × 12 resource elements including 7 OFDM symbols in the time domain and 12 subcarriers in the frequency domain, but the number of OFDM symbols and the number of subcarriers in the resource block is equal to this. It is not limited. The number of OFDM symbols and the number of subcarriers can be variously changed according to the length of the CP, frequency spacing, and the like. For example, the number of OFDM symbols is 7 for a normal CP and the number of OFDM symbols is 6 for an extended CP. The number of subcarriers in one OFDM symbol may be selected and used among 128, 256, 512, 1024, 1536 and 2048.

4 shows a structure of a downlink subframe.

The downlink subframe includes two slots in the time domain, and each slot includes seven OFDM symbols in the normal CP. The leading up to 3 OFDM symbols (up to 4 OFDM symbols for 1.4Mhz bandwidth) of the first slot in the subframe are the control regions to which control channels are allocated, and the remaining OFDM symbols are the PDSCH (Physical Downlink Shared Channel). Becomes the data area to be allocated.

PDCCH is a resource allocation and transmission format of downlink-shared channel (DL-SCH), resource allocation information of uplink shared channel (UL-SCH), paging information on PCH, system information on DL-SCH, random access transmitted on PDSCH Resource allocation of upper layer control messages such as responses, sets of transmit power control commands for individual UEs in any UE group, activation of Voice over Internet Protocol (VoIP), and the like. A plurality of PDCCHs may be transmitted in the control region, and the terminal may monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive CCEs. CCE is a logical allocation unit used to provide a PDCCH with a coding rate according to a state of a radio channel. The CCE corresponds to a plurality of resource element groups. The format of the PDCCH and the number of bits of the PDCCH are determined according to the correlation between the number of CCEs and the coding rate provided by the CCEs.

The base station determines the PDCCH format according to the DCI to be sent to the terminal, and attaches a CRC (Cyclic Redundancy Check) to the control information. In the CRC, a unique identifier (RNTI: Radio Network Temporary Identifier) is masked according to an owner or a purpose of the PDCCH. If the PDCCH is for a specific terminal, a unique identifier of the terminal, for example, a C-RNTI (Cell-RNTI) may be masked to the CRC. Alternatively, if the PDCCH is for a paging message, a paging indication identifier, for example, P-RNTI (P-RNTI), may be masked to the CRC. If the PDCCH is for a System Information Block (SIB), the system information identifier and the System Information-RNTI (SI-RNTI) may be masked to the CRC. A random access-RNTI (RA-RNTI) may be masked to the CRC to indicate a random access response that is a response to the transmission of the random access preamble of the UE.

5 shows a structure of an uplink subframe.

The uplink subframe may be divided into a control region and a data region in the frequency domain. The control region is allocated a Physical Uplink Control Channel (PUCCH) for transmitting uplink control information. The data region is allocated a physical uplink shared channel (PUSCH) for transmitting data. When indicated by the higher layer, the terminal may support simultaneous transmission of the PUSCH and the PUCCH.

PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers in each of the first slot and the second slot. The frequency occupied by the resource block belonging to the resource block pair allocated to the PUCCH is changed based on a slot boundary. This is called that the RB pair allocated to the PUCCH is frequency-hopped at the slot boundary. The terminal may obtain a frequency diversity gain by transmitting uplink control information through different subcarriers over time. m is a location index indicating a logical frequency domain location of a resource block pair allocated to a PUCCH in a subframe.

The uplink control information transmitted on the PUCCH includes a hybrid automatic repeat request (HARQ) acknowledgment (ACK) / non-acknowledgement (NACK), a channel quality indicator (CQI) indicating a downlink channel state, and an SR for an uplink radio resource allocation request. (Scheduling Request).

PUSCH is mapped to an uplink shared channel (UL-SCH) which is a transport channel. The uplink data transmitted on the PUSCH may be a transport block which is a data block for the UL-SCH transmitted during the TTI. The transport block may be user information. Alternatively, the uplink data may be multiplexed data. The multiplexed data may be a multiplexed transport block and control information for the UL-SCH. For example, control information multiplexed with data may include CQI, PMI (Precoding Matrix Indicator), HARQ, RI (Rank Indicator), and the like. Alternatively, the uplink data may consist of control information only.

Hereinafter, a method for reducing inter-cell interference (ICI) in a heterogeneous network environment and a heterogeneous network communication environment will be described.

6 shows an example of a heterogeneous network communication environment.

Basically, heterogeneous network refers to a communication environment in which a base station having a relatively small service coverage coexists in a service coverage of an existing base station. There may be multiple cells in a single cellular coverage, and a cell having a relatively low service coverage may be one of a femto cell, a pico cell, a hotspot, or a relay station (RS). Can be.

Referring to FIG. 6, a heterogeneous network communication environment includes at least one macro cell and at least one femto cell 61 and / or at least one pico cell 62. The service coverage of the macro cell 60 is greater than the service coverage of the femto cell 61 or pico cell 62, and the service coverage of the femto cell 61 and the service coverage of the pico cell 62 are of the macro cell 60. It may be included in service coverage. The macro cell 60 transmits the object signal from the macro cell 60 to the macro terminal receiving the service, the femto cell 61 transmits the object signal from the femto cell 61 to the serviced femto terminal, and the pico cell 62. ) Transmits the destination signal from the pico cell 62 to the pico terminal receiving the service. On the other hand, in general, the transmit power of the macro cell 60 is stronger than the transmit power of the femto cell 61 or pico cell 62. Accordingly, the macro cell 60 may act as interference to the femto terminal serviced from the femto cell 61 or the pico terminal serviced from the pico cell 62. In particular, the terminal located at the boundary of the femto cell 61 or pico cell 62 may act as interference.

In order to solve the inter-cell interference problem between the macro cell and the femto cell or pico cell, a frequency domain based solution and a time domain based solution may be proposed. In the time domain-based solution, radio resources used by the macro cell and femto cell or pico cell are separated from each other in the time domain. In the frequency domain-based solution, the radio resources used by the macro cell and femto cell or pico cell are frequency. Can be separated from one another in the region. Hereinafter, a single cell having a small service coverage will be collectively referred to as a pico cell, but is not limited thereto.

7 illustrates an embodiment of a time domain based solution for reducing intercell interference in a heterogeneous network communication environment.

7- (a) shows a case in which a macro cell acts as an interference to a pico terminal located at a boundary of a pico cell in a heterogeneous network communication environment. The heterogeneous network communication environment includes a macro cell 70 and a pico cell 71, wherein the macro cell 70 transmits a target signal to the macro terminal 73 and the pico cell 71 to the pico terminal 72, respectively. do. Since the intensity of the transmit power of the macro cell 70 is stronger than that of the pico cell 71, the macro cell 70 is located with respect to the pico terminal 72 located at the boundary of the service coverage of the pico cell 71. Acts as interference.

7- (b) shows an example of a configuration of a DL subframe according to a time domain based solution. Referring to FIG. 7- (b), subframe # 2 and subframe # 6 of the macro cell are set to an almost blank subframe (ABS). The macro cell may configure the ABS according to the situation, and in the subframe set to the ABS, only the minimum control information may be transmitted without transmitting data. The macro cell may transmit information about the set ABS to the pico cell through the X2 interface. In this case, the information on the ABS may be a 40-bit bitmap. The pico cell may classify pico terminals located at the border of the pico cell, and may schedule the corresponding pico terminal only in a subframe set to ABS to avoid inter-cell interference.

 The control signal or control channel that can be transmitted in a subframe set to ABS includes a cell-specific reference signal (CRS), a first synchronization signal (PSS), and a second synchronization signal (SSS) It may be a synchronization signal (PBCH), a physical broadcast channel (PBCH), a system information block 1 (SIB1), a paging or positioning reference signal (PRS). Other signals are not transmitted in the subframe set to ABS. In addition, if a multicast broadcast single frequency network (MBSFN) subframe that does not transmit data is set to ABS, the MBSFN subframe may be a complete empty region in which no CRS is defined. In addition, the MBSFN subframe for transmitting data cannot be set to ABS.

As described above, the time domain based inter-cell interference solving method through the ABS has a disadvantage in that real-time traffic is not supported because the pico terminal located at the boundary of the pico cell is scheduled only in a subframe set to ABS. In addition, when the ABS is not configured according to the situation of the macro cell, the pico terminal located at the boundary may have a disadvantage in that it does not receive scheduling at all.

8 shows an air interface structure of layer 2 or more in 3GPP LTE. Referring to FIG. 8, a plurality of macro BSs 80 and pico BSs 81 are connected by an X2 interface, and each macro BS 80 and an MME / S-GW 82 or a pico BS 81 and an MME are connected. The / S-GW 82 is connected to the S1 interface.

9 illustrates an embodiment of a frequency domain based solution for reducing intercell interference in a heterogeneous network communication environment.

Referring to FIG. 9, the macro cell and the pico cell determine a size of a required control region based on a load ratio or a user distribution within a cell, and transmit a PDCCH by setting a control region within a frequency band independent of each other. That is, the control region of the macro cell and the control region of the pico cell do not overlap each other. The macro cell and the pico cell broadcast information about each control area to all users in the cell, the macro terminal only transmits the control information transmitted in the control area of the macro cell, and the pico terminal transmits the information in the control area of the pico cell. Only control information can be read.

When the inter-cell interference problem is solved by separately setting the control region of the macro cell and the control region of the pico cell as described above, only the inter-cell interference in the control region is reduced and the inter-cell interference problem in the data region is not solved. In addition, since the macro cell and the pico cell have to use the limited control area separately, there may be a problem that the control area that can be used is insufficient. In addition, since information on setting of the control area of the macro cell and the control area of the pico cell must be transmitted to all users in the cell, there is a disadvantage in that the operation of the dynamic control area is impossible. In other words, resources are not used efficiently.

As described above, both a time domain based solution and a frequency domain based solution for reducing inter-cell interference have disadvantages, and have limitations that can be limitedly applied in a specific communication environment. Accordingly, there is a need to propose a method for reducing inter-cell interference, which can be universally applied regardless of a communication environment. Hereinafter, a method of reducing inter-cell interference between a macro cell and a pico cell will be described as an example, but is not limited thereto. In addition, the inter-cell interference reduction method described below may be applied in combination with an existing time domain based solution and a frequency domain based solution.

In the next generation mobile communication system, many researches are being conducted to increase cell coverage and increase transmission rate by using multiple transmit / receive antenna communication technology. In particular, the multi-antenna technology may form a transmission beam for each layer by linearly processing each layer of multiple-input multiple-output (MIMO) using precoding. Precoding schemes used in MIMO include open-loop and closed-loop schemes, and 3GPP LTE and LTE-A support both schemes. Precoding may be expressed as Equation 1 below. In this case, it is assumed that cyclic delay diversity (CDD) is not applied to the transmission signal.

&Quot; (1) "

Table 1 and Table 2 show the precoding matrix defined in 3GPP LTE and LTE-A according to the antenna port configuration. Each precoding matrix is orthogonal to each other. In addition, since the base station transmits a precoding matrix indicator (PMI) through a DL grant transmitted through the PDCCH, the terminal may decode the received signal by obtaining precoding information applied to the received signal.

TABLE 1

TABLE 2

Table 1 shows a precoding matrix defined for each layer when the number of layers is two and table 2 when the number of layers is four.

Hereinafter, a method of transmitting control information for reducing inter-cell interference proposed by the embodiment will be described.

The macro cell and the pico cell may communicate with each other through an X2 interface. The macro cell and the pico cell may exchange PMI configuration information with each other through the X2 interface. In addition, the macro cell may transmit ABS configuration information consisting of a 40-bit bitmap to the pico cell.

Meanwhile, the macro cell and the pico cell may receive feedback about PMI configuration information or channel quality indicator (CQI) obtained by the terminal. In this case, the PMI and / or the CQI may be measured in subband units by dividing the entire frequency band into several subbands. In general, the UE may feed back the CQI of the subband (optimal subband) having the best measured value among the CQIs measured in units of a plurality of subbands to a macro cell or a pico cell. In addition, a PMI having the best average signal-to-interference noise ratio (SINR) or spectral efficiency for the entire frequency band may be selected and fed back to the macro cell or pico cell. The base station may schedule the terminal by applying the feedback PMI to the optimal subband of the terminal based on the feedback PMI and / or CQI. Alternatively, the macro cell and the pico cell may directly obtain PMI configuration information or information on CQI. The pico cell may measure the signal received from the macro cell by itself to obtain PMI configuration information or CQI information for each subband. Also, the macro cell or pico cell may periodically acquire PMI configuration information by analyzing PMI usage information. At this time, the base station may analyze the PMI usage information mainly used according to the location of the terminal.

10 shows an example of a PMI index for each subband of a macro cell forming a beam in a pico cell direction.

If the channels between the macro cell and pico cell are uncorrelated, that is, if the channel between the macro cell and pico cell is rich scattering or independent and identically distributed (IID), select by subband in the macro cell The PMIs are likely to be different from each other. In addition, the macro cell can use the entire PMI evenly. Accordingly, PMIs forming beams for each subband in the same direction of the pico cell direction may be different from each other. Referring to FIG. 10, when the total system bandwidth consists of L subbands, each subband may use a different PMI. The PMI table of FIG. 10 may be obtained by accumulating information on a PMI used by each terminal for each subband from terminals in a cell.

Meanwhile, when the channel between the macro cell and the pico cell is partially or completely correlated, PMIs selected for each subband in the macro cell may be the same. In addition, the number of subbands using the same PMI may increase according to the channel correlation. In particular, when the channel correlation is 1, the maximum value may be all subbands constituting the entire system bandwidth. The macro cell may use only some PMIs, so that the PMIs forming the beams in the pico cell direction for each subband may coincide.

In order to reduce inter-cell interference, the first cell may transmit PMI usage information for each time frequency resource to the second cell. In this case, the PMI usage information may indicate PMI information that is limited in time frequency resources such as some subframes or subbands.

For example, a macro cell may periodically or aperiodically configure a subframe that does not use non-preferred PMIs of the pico cell for a pico terminal that is serviced by a specific pico cell, and the macro base station may configure information about non-preferred PMIs. Alternatively, information about a subframe not using unpreferred PMIs may be transmitted to the corresponding pico cell. Alternatively, the macro cell may constitute a PMI subset according to the configuration of pico cells within the coverage of the macro cell. For example, when using a 3-bit codebook, the PMI subset # 0 = {PMI # 0, # 1, # 5, # 6}, the PMI subset # 1 = {PMI # 2, # 3, PMI subsets can be configured as shown in # 4, # 7}, and PMI subsets # 0 and # 1 can be alternately used for each subframe within a specific frame. A specific frame that transmits PMI subsets alternately may be referred to as a PMI subset rotating frame. At this time, the macro cell may transmit configuration information of the PMI subset, PMI subset rotation frame setting information, and PMI subset information rotated within the PMI subset rotation frame to the pico cell.

11 shows an embodiment of PMI usage information according to the proposed method for transmitting control information for reducing inter-cell interference.

The transmitted PMI usage information may be information about a PMI used by the first cell transmitting the PMI usage information. That is, the first cell may transmit information on the PMI to be used for each DL subframe to the second cell. Referring to FIG. 11, when a total of 16 PMIs are present, the first cell includes all PMIs (PMI # 1 to # 9) in subframes # 0, # 2, # 3, # 4, # 5, # 7, # 8, and # 9. Use # 16). On the other hand, only PMI # 1 to # 5 are used in subframes # 1 and # 6. Accordingly, the second cell may allocate DL resources to subframes # 1 and / or # 6 for UEs that are not greatly affected by the use of PMI # 1 to # 5 of the first cell. Since the UEs allocated with DL resources in subframes # 1 and / or # 6 have different interference levels for each subframe, the CQI may be measured only in either subframe # 1 or # 6. Alternatively, the transmitted PMI information may be information on a PMI not to be used by the first cell transmitting the same.

The transmitted PMI usage information may be information about a PMI that can be used by a second cell that receives the PMI usage information. 11 can also be applied in this case. When the total number of PMIs is 16, the second cell may use PMIs # 1 to # 5 in subframes # 1 and # 6, and all PMIs may be used in other subframes. The second cell receiving the PMI usage information may allocate DL resources for the UE using PMI # 1 to # 5 in subframes # 1 and / or # 6. Since UEs allocated to DL resources in subframes # 1 and / or # 6 have different interference levels for each subframe, the CQI may be measured only in any one of subframes # 1 and # 6. Alternatively, the transmitted PMI information may be information about a PMI that the second cell that receives it does not want to use.

The PMI usage information transmitted by the first cell to the second cell may be configured in various ways.

1) PMI usage information can be configured by directly listing used or unused PMIs. In this case, PMI usage information may be configured using bitmaps as many as PMI, or PMI usage information may be configured by listing all corresponding PMIs such as PMI # 1, PMI # 3, PMI # 9, ....

2) PMI usage information can be configured with several PMIs and the number of PMIs. As a result, the size of the transmitted information can be reduced compared to the case of directly arranging the PMI. In this case, as many PMIs as the number of PMIs among the smallest or largest PMIs having a correlation value between each of several PMIs and the corresponding PMI may be transmitted by PMI usage information. For example, when the PMI # 1, # 3 and the number {2,1} of the PMI are transmitted according to the PMI usage information, the second cell receiving the PMI usage information has 2 having the smallest correlation value with the PMI # 1. PMI # 15, which is the one having the smallest correlation value with PMI # 9, # 10 and PMI # 3, which are PMIs, can be recognized together with PMI # 1, # 3. In addition, if only the number of PMIs {2} is included in the PMI usage information, the second cell may recognize two PMIs having the smallest correlation values with PMI # 1 and # 3, respectively.

3) PMI usage information can be configured with several PMIs and thresholds. For example, PMI usage information may be configured with PMI # 1, # 3 and thresholds {0.2, 0.1}. In this case, the second cell may recognize PMI # 5 and # 7 having a correlation value of 0.2 or less with PMI # 1, and also know PMI # 15 having a correlation value of 0.1 or less with PMI # 3. In addition, the threshold value may be set in common for a plurality of PMIs.

On the other hand, when the PMI of the first cell is composed of two or more PMI, the first cell may inform the second cell of the usage information of all the PMI, only the usage information of some PMI of the two or more PMI to the second cell You can also tell. For example, when the precoding matrix W = W ₁ W ₂ of the first cell is configured, the first cell may transmit usage information of W to the second cell, or may transmit only usage information of W ₁ to the second cell. . In this case, the UE receiving the service of the second cell may feed back information corresponding to W ₁ to the second cell.

Alternatively, in order to reduce inter-cell interference, the first cell may transmit antenna usage information for each time frequency resource to the second cell. In the following description, the antenna may be replaced with not only a physical antenna but also an antenna port, an antenna node, an antenna group, an antenna node group, a pilot, a reference signal, a channel state information (CSI) reference signal, a CRS, a midamble, and the like. have.

12 shows an embodiment of antenna usage information according to a method for transmitting control information for reducing inter-cell interference.

The transmitted antenna usage information may be information about an antenna used by the first cell transmitting the antenna usage information. That is, the first cell may transmit information on the antenna to be used for each DL subframe to the second cell. Referring to FIG. 12, when there are 16 antennas in total, the first cell includes all antennas (antennas # 1 to 9) in subframes # 0, # 2, # 3, # 4, # 5, # 7, # 8, and # 9. Use # 4). On the other hand, only antennas # 2 to # 4 are used in subframes # 1 and # 6. The second cell may use the received antenna usage information for scheduling of the terminal. For example, the second cell may allocate DL resources in subframe # 1 and / or # 6 for a terminal that does not receive much interference from antennas # 2 to # 4 of the macro cell. Since UEs allocated to DL resources in subframes # 1 and / or # 6 have different interference levels for each subframe, the CQI may be measured only in any one of subframes # 1 and # 6. On the other hand, before the information about the antenna used by the first cell is transmitted, the UE receiving the service of the second cell may feed back information about the antenna of the first cell with a large or small interference to the second cell. The 2 cell may transmit the interference antenna information received from the terminal or the interference antenna information directly measured by the second cell to the first cell.

In addition, the transmitted antenna usage information may be information on an antenna available to the second cell receiving the antenna usage information. 12 can also be applied in this case. The second cell receiving the antenna usage information may allocate DL resources for the UE using antennas # 2 to # 4 in subframes # 1 and / or # 6. Since UEs allocated to DL resources in subframes # 1 and / or # 6 have different interference levels for each subframe, the CQI may be measured only in any one of subframes # 1 and # 6. On the other hand, before the information about the antenna that can be used by the second cell is transmitted, the first cell may receive the feedback of the interference antenna information from the terminal receiving the service of the first cell or directly measure the interference antenna.

The antenna usage information may be constructed by directly listing the antennas used or not used. For example, assuming that the number of antennas of the first cell is four and the antenna usage pattern is repeated every 10 subframes, the antenna usage information transmitted by the first cell to the second cell may be 40 bits. . In the case of FIG. 12, antenna usage information may be [1111 0111 1111 1111 1111 1111 0111 1111 1111 1111]. That is, the 40-bit antenna usage information may indicate that antenna # 1 of subframes # 1 and # 6 is used or not used. Alternatively, in order to reduce the size of the antenna usage information, a bitmap indicating a subframe in which some antennas are not used and a bitmap indicating an antenna used or not used in the corresponding subframe may be distinguished and transmitted. In the case of FIG. 12, a bitmap indicating a subframe in which some antennas are not used may be [0100001000], and a bitmap indicating an antenna used or not used in the subframe may be [01110111].

The inter-cell interference reduction method based on the above-described PMI usage information or the inter-cell interference reduction method based on the antenna usage information may have different effects depending on the antenna configuration of the second cell receiving the usage information. For example, if the correlation value between antennas of the second cell is high, the inter-cell interference reduction method based on the PMI usage information may effectively reduce the inter-cell interference while lowering the performance of the second cell. On the other hand, when the correlation value between the antennas of the second cell is small or the antennas are spread in the cell, the inter-cell interference reduction method based on the antenna usage information is more efficient. Accordingly, for more efficient inter-cell interference reduction, it is preferable that a terminal receiving the service of the first cell selects one of two inter-cell interference reduction methods and informs the first cell. In this case, the UE should know in advance information about a pilot of the second cell, that is, a reference signal, a CRS, a CSI-RS, a midamble, an antenna port, and the like. Alternatively, the first cell may instruct the terminal to provide feedback corresponding to one of two inter-cell interference reduction methods, and for this purpose, the second cell first selects one of two inter-cell interference reduction methods and informs the first cell. Can be.

13 shows an embodiment of a method for transmitting control information for reducing inter-cell interference.

In operation S100, the first cell determines a method for reducing inter-cell interference. In this case, the inter-cell interference reduction method may be any one of the method based on the PMI usage information described above or the method based on the antenna usage information. In operation S110, the first cell may transmit precoding information or antenna information for each time frequency resource to the second cell based on the determined intercell interference reduction method. In step S120, the second cell communicates with the terminal by allocating resources based on the received precoding information or antenna information.

14 is a block diagram of a wireless communication system in which an embodiment of the present invention is implemented.

The first base station 800 includes a processor 810, a memory 820, and an RF unit 830. Processor 810 implements the proposed functions, processes, and / or methods. Layers of the air interface protocol may be implemented by the processor 810. The memory 820 is connected to the processor 810 and stores various information for driving the processor 810. The RF unit 830 is connected to the processor 810 to transmit and / or receive a radio signal.

The second base station 900 includes a processor 910, a memory 920, and an RF unit 930. Processor 910 implements the proposed functions, processes, and / or methods. Layers of the air interface protocol may be implemented by the processor 910. The memory 920 is connected to the processor 910 and stores various information for driving the processor 910. The RF unit 930 is connected to the processor 910 to transmit and / or receive a radio signal.

Processors 810 and 910 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory 820, 920 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and / or other storage device. The RF unit 830 and 930 may include a baseband circuit for processing a radio signal. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above. The module may be stored in the memory 820, 920 and executed by the processor 810, 910. The memories 820 and 920 may be inside or outside the processors 810 and 910, and may be connected to the processors 810 and 910 by various well-known means.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (15)

A method of transmitting control information by a first base station in a wireless communication system,
Determine a method of reducing inter-cell interference,
And transmitting any one of precoding information or antenna information for each time frequency resource to a second base station based on the determined inter-cell interference reduction method. The method of claim 1,
The precoding information is a method of transmitting control information, characterized in that it indicates a precoding matrix indicator (PMI) used by the first base station for each subframe or a PMI that the second base station can use for each subframe. The method of claim 2,
The precoding information comprises a bitmap based on the total number of PMI. The method of claim 2,
The precoding information includes an index of at least one PMI and a number of PMIs based on the at least one PMI. The method of claim 2,
The precoding information includes an index of at least one PMI and a threshold based on the at least one PMI. The method of claim 1,
And the antenna information indicates an antenna used by the first base station for each subframe or an antenna that can be used by the second base station for each subframe. The method according to claim 6,
When the antenna information indicates the antenna used by the first base station for each subframe,
Receiving antenna interference information measured by the terminals serviced by the second base station from the second base station,
The antenna information is a control information transmission method, characterized in that based on the received antenna interference information. The method according to claim 6,
When the antenna information indicates an antenna that the second base station can use for each subframe,
Receiving antenna interference information measured by the terminals serviced by the first base station or directly obtaining antenna interference information,
And the antenna information is based on the received or acquired antenna interference information. The method according to claim 6,
The antenna information comprises a bitmap based on the total number of antennas. The method of claim 1,
The second base station further comprises allocating downlink resources to the terminal based on the received precoding information or antenna information. The method of claim 10,
And the second base station communicates with the terminal through a downlink resource allocated to the terminal. The method of claim 1,
The first base station is a base station providing a service to a macro cell (macro cell),
And the second base station is a base station that provides a service to a femto cell or a pico cell whose service coverage is included in the service coverage of the macro cell. In a wireless communication system,
RF (radio frequency) unit for transmitting or receiving a radio signal; And
Including a processor connected to the RF unit,
The processor comprising:
Determine a method of reducing inter-cell interference,
And a first base station configured to transmit one of time-coding resource-specific precoding information or antenna information to a second base station based on the determined inter-cell interference reduction method. The method of claim 1,
Wherein the precoding information indicates a precoding matrix indicator (PMI) used by the first base station for each subframe or a PMI that the second base station can use for each subframe. The method of claim 13,
The antenna information is a first base station characterized by indicating the antenna that the first base station is used for each subframe or the antenna that the second base station can be used for each subframe.

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